1. Field of the Invention
This invention relates to fiber-optic communication systems. More specifically, this invention relates to bidirectional signal transmission within such communication systems.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art
In certain remote-guidance systems communication with a guided vehicle is facilitated by an optical fiber linking the vehicle with a control station. The optical fiber is typically wound around a bobbin, or secured by other means capable of dispensing the fiber as the vehicle travels downrange. An optical carrier of a first wavelength is used to transport commands from the control station to the vehicle, while data from the vehicle is impressed upon an optical carrier of a second wavelength and carried by the fiber to the control station. Hence, bidirectional communication is effectuated in conventional fiber-optic systems by using optical energy at a pair of wavelengths to carry information in opposing directions.
Unfortunately, signal loss induced by the connecting fiber is typically minimized only at relatively long optical wavelengths. Since the optical carriers propagating in opposite directions along the link must generally be separated by a sufficient wavelength spacing to prevent channel cross-talk, the wavelength of both carriers may not be chosen to be near those of minimal signal loss. Accordingly, the signal transmission range of conventional dual-wavelength bidirectional optical fiber communication links is less than would be possible for a fiber link operative exclusively at a single wavelength of minimal signal loss.
Fiber-induced signal loss generally necessitates intermediate amplification in long range systems. However, in the conventional dual wavelength systems described above the transmitted light energy may not be directly amplified. This limitation arises because optical amplifiers are tuned to a single optical wavelength in order to provide maximum amplification. Accordingly, complex and expensive optical repeaters are used in lieu of optical amplifiers in conventional fiber-optic communication links. Optical repeaters operate by first converting the signals carried by the light energy back to the electrical domain. Next, these extricated electrical signals are superimposed upon a separately generated optical carrier. In addition, optical repeaters complicate system design as they often need to be included at multiple locations in very long-range fiber-optic links.
It follows that a need in the art exists for a long-range fiber-optic communication link which is operative at an optical carrier wavelength of minimal loss, and which maintains signal intensity through direct optical amplification rather than through the utilization of repeaters.